Feb 2015 -0.35 -0.35 0.01 ΨMD Feb 2014 -1.38 -1.44 0.09 Feb 2015 -1.12 -1.15 0.05 † * <0.05, ** <0.01, *** <0.001 § geometric means
The afternoon value of Vapour Pressure Deficit (VPD) was 1.95 kPa in 2014 and 1.56 kPa in 2015.
Table 12. The significance† of floor management treatment effects on the early afternoon leaf
photosynthetic rate (A, µmol CO2/m2.s) and stomatal conductance (g, mol H2O/m2.s) in February 2015
and mid-day and pre-dawn leaf water potentials (ΨMD and ΨPD, respectively, MPa) in February 2014
and 2015. Parameter Treatment LSD A B C D E A 2015 10.2 10.4 10.5 10.4 10.4 1.7 g 2015 0.062 0.058 0.063 0.062 0.066 0.009 ΨPD 2014 -0.33 -0.32 -0.33 -0.30** -0.32 0.03 2015 -0.35 -0.34* -0.34* -0.33** -0.33** 0.01 ΨMD 2014 -1.44 -1.45 -1.45 -1.29** -1.47 0.09 2015 -1.15 -1.13 -1.13 -1.09* -1.12 0.05 † * <0.05, ** <0.01, *** <0.001
Treatments testing changes to vineyard floor management had no effect on the 2015 measures of either leaf photosynthetic rate or stomatal conductance, with averages of 10.4 µmol CO2/m2.s and 0.062 mol H2O/m2.s, respectively.
Treatment D vines had significantly higher pre-dawn (-0.32) and midday (-1.19) LWP’s in both assessment years, suggesting reduced stress relative to both control treatments, Table 12. In the 2015 season, Treatments B, C and E midday readings also differentiated from Treatment A, particularly Treatment E which was also significantly higher than the non-ripped Treatment F. Soil moisture monitored through the 2015 season showed Treatments D and E as being 7 and 12% higher in soil water contents relative to the ripped controls, Treatment A (data not shown). This trend agrees with the modelled predictions, described in Appendix G, and may explain the reduced leaf water potentials reported by the rainfall redirection treatments. Both Treatments D and E incorporated an impermeable plastic layer in their construction which likely reduced evaporative losses and so maintained soils moistures at higher levels.
1.3.5.2
Effects on vegetative growth
Between treatment establishment and the end of the 2013 growing season, vines received <40 mm of rain. Thus, measures of pruning weights in June 2013 reflected the uniformity of vine recovery from treatment establishment rather than the influence of rainfall redirection treatments. Cane weights were equivalent at this time at 1.65 kg/vine, Figure 16. Uniformity of vigour in this first year aligns with that of yield and fruit maturity trends measured in March 2013, Table 9.
The 2013/14 growing season saw increased vigour in treatments with the greatest propensity for redirecting rain. Irrigation was below average through 2013/14 and Treatment D benefited from its ability to redirect rain from the mid-row towards the under-vine soils with 14% greater pruning weights (1.42 kg/vine) than Treatment A (1.22 kg/vine) and 21% greater vigour than the non-ripped control, Treatment F (1.12 kg/vine). Treatment E was also 13% more vigorous than Treatment F with pruning weights at 1.3 kg/vine. These trends match within season vigour assessments as measured by Leaf Area Index (LAI), Figure 17.
Figure 16. The effects of vineyard floor management treatments on vine vigour as measured by winter pruning weights (kg of cane/vine). July 2013 and July 2014. Vertical bars indicate standard errors of means.
While winter pruning weights are a recognised measure of a vine’s vigour through the preceding growing season, this destructive method does not offer any insight into the progression of growth through the season. LAI is a non-destructive measure of plant vigour that can complement end of season pruning weights. Measures of LAI were collected at three growth stages in 2013/14 and 2014/15 viz., Flowering, Veraison and Harvest. Measures of LAI suggest that there was little difference between
June 2013 A B C D E F P runi ng w ei g ht / v ine (k g ) 1.0 1.5 2.0 July 2014 A B C D E F 1.0 1.5 2.0
(veraison). In the approach to harvest, Treatment D and E vines retained and/or produced more leaf cover than control vines.
Figure 17. The effects of vineyard floor management treatments on vine vigour as measured by Leaf Area Index through the 2013/14 and 2014/15 growing seasons. Vertical bars indicate standard errors of means.
Through this same season, Treatment C vines reported lower LAI values but ultimately caught up to the control vines. A single measure of LAI in non-ripped controls, Treatment F, saw the first signs of vigour differences between the ripped, Treatment A, and non-ripped, Treatment F, controls, Figure 17. This trend was reflected in the July 2014 pruning weights, Figure 16. Following the heavy crop of the 2013/14 irrigation season, trial vines commenced the 2014/15 with lower vigour, averaging 1.65 LAI as opposed to the 1.81 of the previous season. This rapidly changed as the mild season combined with a lower crop load and a more generous irrigation schedule (35% greater than previous seasons) to encourage rapid vegetative growth. At the January 2015 (veraison) sampling point, average LAI was in excess of 3 and Treatment E had differentiated from control vines. Treatment D vigour was not as precocious as the previous season and was likely recovering from the previous season’s high vigour and heavy crop loads. All treatments were significantly more vigorous than the non-ripped control, Treatment F.
1.3.6
Numerical modelling of vineyard floor management changes
and their predicted effect on soil water and solute dynamics
The project had originally been written to support a PhD candidate in answering questions around irrigating viticulture with recycled wastewater, with specific reference to the interaction between slightly saline wastewater and the physical and chemical properties of soils. Unfortunately, a suitably qualified PhD candidate was not identified through the course of the project. However, SARDI and University of Adelaide staff did collect numerous intact cores in 2013 which were subsequently analysed by the University for their physical and chemical properties, Appendix I.Nov-13 Jan-14 Mar-14
L AI 1.0 1.5 2.0 2.5 3.0 3.5 A B C D E F
Nov-14 Jan-15 Mar-15 1.0 1.5 2.0 2.5 3.0 3.5
In lieu of the PhD, SARDI nominated to make use of the University’s field data in the construction of numerical modelling domains that would add the value to both SARDI’s and the University’s field measurements. At the same time, SARDI constructed modelling domains for the Padthaway irrigation district (saline groundwater) and the Loxton irrigation district (non-saline surface water). Results from these three models are described in Appendix G and extend the usefulness of the current field trial beyond the McLaren Vale recycled wastewater irrigation district to other soils, climates and irrigation sources.
The conceptual modelling analysis compared Treatments A, B, D and E. A summary of the McLaren Vale modelling component follows.